Sheet diverters may range from the collating apparatus associated with an office copier, to sheet or web handling devices employed in the manufacture of paperboard articles, to sheet diverters specifically adapted to collate signatures to be used in binding or otherwise assembling books, magazines or newspapers. Each of these environments presents a somewhat different challenge in designing an efficient diverter or collator, but the same objective tends to dominate the entire class of apparatus, namely, accurately routing selected flexible webs or ribbon sections along a desired collating path to achieve a desired order.
In the printing industry, a desired image is repeatedly printed on a continuous web or substrate such as paper. The ink is dried by running the web through curing ovens. In a typical printing process, the web is subsequently slit (in the longitudinal direction which is the direction of web movement) to produce a plurality of continuous ribbons. The ribbons are aligned one on top of the other, folded longitudinally, and then cut laterally to produce a plurality of multi-paged, approximately page-length web segments, termed signatures. A signature can also be one printed sheet of paper that has or has not been folded. It is often desirable to transport successive signatures in different directions. In general, a sheet diverter operates to route a signature along a desired one of a plurality of paths.
A sheet diverter in a folder at the end of a printing press line must be operable at the high speeds of the press line, typically in excess of 2,000-2,500 feet per minute (fpm). It is desirable to run both the press and folder at the highest speed possible in order to produce as many printed products as possible in a given amount of time. However, the physical qualities of paper or similar flexible substrates moving at a too high rate of speed often results in whipping, dogearring, tearing, or bunching of the substrate. For example, the sudden impact force between the leading edge of a signature and a diverter wedge may result in the leading edge of the signature being damaged. Similarly, the trailing edge of a signature may slap against the top vertex edge of a diverter wedge, resulting in damage to the trailing edge. The trailing edge of the signature may tear, or be unintentionally folded on the corners. Damaged signatures may be of unacceptable quality and may also lead to jams in the folder, resulting in downtime and repair expense.
Many of the foregoing defects become more prevalent above certain speeds of the printing press and folder. For example, such defects may occur when the press is run at a high rate of speed, say greater than 2,500 fpm, but may not occur when the press is run at a slower speed, for example, 2,200 fpm. As machine speeds increase, it becomes increasingly more and more important to provide a system which allows for individual signatures to be directed down any one of a plurality of selected collation paths without damaging the leading or trailing edge of each signature.
A sheet diverter for signature collation and a method thereof is described in U.S. Pat. No. 4,729,282, which is hereby incorporated by reference. U.S. Pat. No. 4,729,282 discloses a sheet diverter including an oscillating diverter guide member that directs successive signatures to opposite sides of a diverter wedge.
At excessively high speeds, the tail end of a signature may be damaged due to whipping of its tail end at the apex of a diverter wedge. At excessive speeds, the diverter may direct the tail end part of a signature to the wrong side of a diverter wedge before the trailing edge of the signature has passed the apex of the diverter wedge. As the trailing edge of the signature reaches the apex, the end of the signature will be "whipped," i.e., tailwhipped, back to the correct side of the diverter wedge to which the preceding portion of the signature traveled along, thereby possibly damaging the tail end of the signature.
Thus, there is a need for a sheet diverter that is capable of operating at high speeds and yet being capable of providing a signature that is acceptable in quality. What is further needed is a sheet diverter for use in the printing industry such that the sheet diverter improves the collation process of printed signatures to prevent or minimize damage to the signatures as the signatures move along one of a plurality of collation paths. Particularly, what is also needed is a sheet diverter that prevents or reduces tailwhip of the end of a signature as the signature travels past the apex of a diverter wedge thereby allowing for greater operational speeds and increasing the quality of each signature.